Potable (i.e., drinking) water is a necessity to which millions of people throughout the world have limited access. Water is often seen as the most basic and accessible element of life, and seemingly the most plentiful. There is no standard for how much water a person needs each day, but experts usually put the minimum at 100 liters for adults. Most people drink two or three liters—less than it takes to flush a toilet. The rest is typically used for cooking, bathing, and sanitation. Adult Americans consume between four hundred and six hundred liters of water each day.
By 2050, there will be at least nine billion people on the planet, the great majority of them in developing countries. If water were spread evenly across the globe, there might be enough for everyone. But rain often falls in the least desirable places at the most disadvantageous times. More than a billion people lack access to drinking water. Simply providing access to clean water could save two million lives each year.
Water purification processes are well known and used throughout the world. Water purification is the removal of contaminants from raw water to produce drinking water that is pure enough for human consumption. Substances that are removed during the process include parasites (such as Giardia or Cryptosporidium), bacteria, algae, viruses, fungi, minerals (including toxic metals such as lead, copper and arsenic), and man-made chemical pollutants. Many contaminants can be dangerous. Other contaminants are removed to improve the water's smell, taste, and appearance.
It is not possible to tell whether water is safe to drink just by looking at it. Simple procedures such as boiling or the use of a household charcoal filter are not sufficient for treating water from an unknown source. Even natural spring water considered safe for all practical purposes in the 1800s must now be tested before determining what kind of treatment is needed. Water emerging from shallow groundwater is usually taken from wells or boreholes. The bacteriological quality can be variable depending on the source.
Typically located in the headwaters of river systems, upland reservoirs are usually sited above any human habitation and may be surrounded by a protective zone to restrict the opportunities for contamination. Bacteria and pathogen levels are usually low, but some bacteria, protozoa or algae will be present. Low land surface waters, such as rivers, canals and low land reservoirs, will have a significant bacterial load and may also contain algae, suspended solids and a variety of dissolved constituents. Surface water may be contaminated with biological and chemical pollutants and may potentially transmit diseases such as diarrhea, dysentery, typhoid, cholera and hepatitis. Because of risk of contamination, surface water should never be used for drinking without treatment and/or disinfection.
Many processes are available for purification of water, with their use depending on the particular contaminants present in the water. Ultrafiltration membranes are a relatively new development; they use polymer film having microscopic pores that can be used in place of granular media to filter water effectively without coagulants. The type of membrane media determines how much pressure is needed to drive the water through and what sizes of micro-organisms can be filtered out. In ultrafiltration, hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in the filter up to about 0.01 microns in size. This removes bacteria and many viruses (which commonly adhere to the bacteria), but not salts (ions), while water and low molecular weight solutes pass through the membrane.
It is desirable to have a reusable water filtration device that attaches to a water bottle or other portable water container and contains an ultrafiltration membrane. The device may provide a design that allows water to pass through the ultrafiltration membrane with minimal pressure. Preferably, the device includes a flushing mechanism that cleans the ultrafiltration membrane without having to disassemble the bottle cap.